The accumulation of cytotoxic Aβ in the brain is considered to be a key pathogenic event contributing to neurodegeneration in Alzheimer's disease (AD). See, Hardy and Selkoe, (2002), Science 297:353-336.
Aβ is a metabolite produced during processing of a large transmembrane glycoprotein, the Aβ precursor protein (APP). The level of Aβ in the brain is controlled by the rate of production from amyloid precursor protein (APP) and the rate of clearance. See, Tanzi et al., (2004) Neuron 43:605-608. Aβ is formed after sequential cleavage of APP, which is a transmembrane glycoprotein of undetermined function. APP can be processed by α-, β- and γ-secretase enzymes, and the Aβ protein is generated by successive action of the β and γ secretase on APP. The C-terminal end of the Aβ peptide is produced by the action of γ-secretase, which cleaves within the transmembrane region of APP to generate a number of isoforms of 39-43 amino acid residues in length. The most common isoforms are Aβ40 and Aβ42. The shorter form (Aβ40) is typically produced by a cleavage reaction that occurs in the endoplasmic reticulum, while the longer form (Aβ42) is typically produced by a cleavage reaction in the trans-Golgi network. See, Nat. Med. 3(9):1016-1020 (1997). The Aβ40 form is the more common of the two, but the Aβ42 is more fibrillogenic and is thus more frequently associated with disease states. Mutations in APP associated with early-onset Alzheimer's have been noted to increase the relative production of Aβ42, and thus one suggested avenue of Alzheimer's therapy involves modulating the activity of β and γ secretases to produce mainly Aβ40—See, Yin, Y. I., et al. (2007) J Biol. Chem. August 10; 282(32):23639-44.
Recently it has been shown that vaccination with Aβ42 as well as passive immunization with anti-Aβ42 antibodies reduced brain Aβ-load and improved behavior in animal models. See, e.g., Schenk et al. (1999) Nature 400:173-177; DeMattos et al., (2001) Proc. Nat'l. Acad. Sci. USA 98:8850-8855; Bard et al. (2000) Nat. Med. 6:916-919; Wilcock et al. (2003) J. Neurosci. 23:3745-3751. Although reduced Aβ deposition (Nicoll et al. (2006) J. Neuropathol. Exp. Neurol. 65:1040-1048) and slower cognitive decline (Hock et al., (2003) Neuron 38:547-554) have been reported in clinical immunization trials involving anti-Aβ42 antibodies in AD patients the trials also showed adverse neuroinflammatory effects as a result of the immunization.
In humans, naturally occurring antibodies against Aβ have been detected in both the cerebrospinal fluid (CSF) and the serum of healthy subjects, while significantly lower anti-Aβ antibody titers have been detected in the in CSF of AD patients. See, Du et al. (2001) Neurology 57:801-805.
Naturally occurring anti-Aβ42 antibodies are detectable in commercially available human IVIG preparations and have been found to modify total Aβ and Aβ42 levels in the CSF. See, Dodel et al. (2002) Ann. Neurol. 52:253-256; and Dodel et al. (2004) J. Neurosurg. Psychiatry 75:1472-1474. Furthermore, it has been shown previously that naturally occurring anti-Aβ antibodies, when isolated from immunoglobulins preparations, inhibit Aβ-induced cytotoxic activity in vitro (Du et al. (2003) Brain 126:1935-1939).
Thus, there exists a need for a method to screen and compare various agents (e.g., different lots of immunoglobulin preparations) for their ability to inhibit Aβ-induced cytotoxicity in vitro. Such a method will allow for the identification of potential drug candidates as well as pre-selection of human plasmatic (IVIG) lots suitable for treating Alzheimer's disease patients. The present invention addresses this and other needs.